NMR techniques have grown extensively over the past forty years, most notably in the medical instrumentation areas where in vivo examination of various parts of the human body can be seen, and in clinical research laboratory uses. In addition there has been some use and interest in the application of these techniques to industrial instrumentation and control tasks. The present invention enables effective utilization (technically and economically) of pulsed NMR techniques in industrial areas to replace or complement existing optical and radiant energy-based and chemical-based and other (e.g. mechanical) instrumentation.
The following is a brief review of nmr [NMR] theory and concepts pertinent to understanding the present invention. [The term "magnetic resonance imaging" (MRI) is an alternative, interchangeable name for "nuclear magnetic resonance" (NMR).] Approximately one third of the elemental isotopes and certain compounds with non-zero spin quantum numbers are magnetically active and suitable for [MRI] nmr detection.
In a simplified model, a spinning isolated nucleus will align itself either with or against a static magnetic field. There will be a nearly equal number of nuclei aligned in each direction since there is only a small energy difference between these two states so a thermal equilibrium exists between these two states. However, statistically there will be a small number of excess nuclei which give rise to nmr signals. The term "nuclei" will subsequently refer only to magnetically active nuclei.
Nuclei in a magnetic field will precess similar to a spinning top because there is an angular acceleration provided by the interaction of the magnetic field and the magnetic moment of the nuclei. This precession occurs in the direction of the magnetic field. Quantum mechanics shows that only a selected number of possible alignments is possible. The precessional frequency is determined by which alignment occurs and the magnetic properties of the nucleus being studied. The fundamental nmr signal is derived from inducing transitions between these different alignments. This is often done by using the magnetic component of an applied RF (radio frequency) signal. When this component is applied perpendicularly to the magnetic field a resonance occurs at a particular RF frequency where transitions between the different alignments happen. This resonance typically occurs in the megahertz frequency ranges when a strong magnetic field is used. This field is in the 1 Tesla (10,000 Gauss) order of magnitude. Resonance being defined as the condition such that, after a short pulse of energy is applied to the sample and a return pulse of decaying energy is generated by the sample, the return signal is essentially an infinite wavelength of a beat frequency product of demodulated excitation and return signals. There are other well understood definitions of resonance known in the art.
Pulsed NMR spectroscopy is described in our above-cited patents. This technique uses a burst or pulse which is designed to excite the nuclei of a particular nuclear species of a sample being measured (the protons, or the like, of such sample having first been precessed in an essentially static magnetic field); in other words the precession is modified by the pulse. After the application of the pulse there occurs a free induction decay (FID) of the magnetization associated with the excited nuclei. Traditional Fourier Transform analysis generates a frequency domain spectrum which can be used to advantage in studying the nuclei of interest. The duration of the pulses, the time between the pulses, the pulse phase angle and the composition of the sample are parameters which affect the sensitivity of this technique. These frequency domain techniques are not easily useable in industrial applications, especially on-line applications.
An object of this invention is an improved measurement system which leads to accurate, fast determination of the types and quantity of the nuclear species of interest.
A further object of this invention is its application to the industrial, on-line problems of measuring and calibrating the controlling processes per se.
Another object of this invention is to utilize time domain analysis in achieving such system.
The principal variables of interest are moisture, oil/fat and polymer crystallinity and density. But other parameters can be measured based on hydrogen or other sensitive species including e.g. sodium and fluorine. It is an object of this invention to accommodate a variety of such measuring tasks.
Another object is to accommodate the dynamics of industrial on-line applications including variations of density, temperature, packing and size factors, friction and static electricity, vibrations and frequent, repetitive, cyclic and non-cyclic measurements.
A further object of the invention is to integrate all the features of accurate, fast determination of the types and quantity of the nuclear species of interest, the use of time domain analysis in such a system, its application to the industrial, on-line problems of monitoring and controlling processes, measuring free and bound water in organic or inorganic substances (based on hydrogen nuclei modified-precession analysis) and other parameter measurement (based on hydrogen or other sensitive species including e.g. fluorine, sodium-23, etc.) accommodating the dynamics of industrial on-line applications including variations of density, temperature, packing and size factors, friction and static electricity, vibration and frequent, repetitive, cyclic and non-cyclic measurements.
A further object of the invention is to use such magnetic resonance techniques in polymer analysis, including crystallinity and density, all with enhanced accuracy and reliability of data obtained and while achieving the necessary practical economies.
A further object of the present invention is to extend those achievements further in relation to industrial on-line processing, and the like, as applied to mixed species (or mixed phases) of NMR-active materials and more particularly foodstuffs and plastics materials (and being applicable to many other NMR-active materials) with a third component such as oils/fats or solvents in addition to two main components (moisture/solids, crystalline/amorphous).